1. Technical Field
The present invention relates to a general purpose computer system, and more particularly, relates to a monitor control device which receives video and synchronizing signals from a host computer to provide a visual display of information on a monitor, and a method for controlling the monitor.
2. Background Art
Conventional monitors, both color and monochrome, typically have built-in control inputs for manual user adjustments of display parameters such as contrast, brightness, picture position including horizontal and vertical positioning, size, tint, color balance, focus, degauss, video cutoff, video gain, tilt, parallelogram, trapezoid distortion adjustment, inter alia. Multi frequency monitors have several control inputs which increase the number of combinations of adjustments that a user can make. These control inputs are typically rotary potentiometers, and may be mounted at different locations around the case of the monitor as determined by each manufacturer. They may be located on the front in plane with the display screen, on the side, in the back, or on top of the case, often behind a small panel where the user may open to access the controls.
In a cathode ray tube (CRT) monitor, the control inputs for contrast and brightness typically interact with video circuitry in the monitor, and modulate the signal by varying electrical potential that effect the formation of an on-screen image. The brightness control, for example, adjusts the level of the scanning electron beam, which in turn makes the on-screen image brighter or less bright. Contrast is the linear relationship between incoming video dot data signal strength and the current screen brightness. In addition to brightness and contrast control inputs, there are also control inputs for position and sizing, which allow the user to alter the position of the display on the screen and to adjust the height and width of the display area on the screen.
Generally, a CRT monitor is connected to a host computer through a video graphics array (VGA) cable which is used to transfer video signals and a dedicated control cable such as a RS232C cable which is used to transfer control information from the host computer to the monitor. When a RS232C cable is used to transfer control information from the host computer to the monitor, an RS232C port must be established between the host computer and an RS232C interface contained in the monitor which typically results in an increase of production cost. In addition, since the control inputs are mounted on the monitor, it is necessary for the user to reach to the monitor, sometimes to different locations around its case, to find the proper control switches of the monitor to operate the switches when the adjustment of any one of the display contrast, brightness, position, size, tint, color balance, focus, degauss, video cutoff, video gain, tilt, parallelogram, and trapezoid distortion is required. Moreover, since the control inputs are mounted on the monitor with a limited number of control switches, it is impossible for the user to control all the monitor functions sometimes.
Recent efforts in the art such as U.S. Pat. No. 5,550,556 for Transmitting Data And Commands To Display Monitors issued to Wu et al., U.S. Pat. No. 5,532,719 for Remote Control Of Display Functions issued to Kikinis, and U.S. Pat. No. 5,457,473 for Image Display Apparatus issued to Arai et al., have endeavored to provide an image display device for adjusting display parameters for a display monitor without having to access control inputs mounted on the monitor. For example, in Wu et al., U.S. Pat. No. 5,550,556, the display parameters are adjusted by way of software control. Similarly, both Kikinis, U.S. Pat. No. 5,532,719 and Arai et al., U.S. Pat. No. 5,457,473 allow the user to input control instructions for adjusting the display picture from an input unit such as a keyboard. While each of these patents has its own merits, I believe that further improvements can still be made to effectively and efficiently control a variety of display functions of the monitor without the use of a RS232C cable and its interface between the monitor and the host computer.